In conventional radio frequency (RF) plasma processing, such as that used during stages of fabrication of many semiconductor devices; RF energy, which may be generated in continuous or pulsed wave modes, may be provided to a substrate process chamber via multiple RF energy sources. Due to mismatches between the impedance of the RF energy source and the plasma formed in the process chamber, RF energy is reflected back to the RF energy sources, resulting in inefficient use of the RF energy and wasting energy, potential damage to the process chamber or RF energy sources, and potential inconsistency/non-repeatability issues with respect to substrate processing.
In process chambers that use dual-level pulsing, load leveling can be performed to compensate for the reflected power such that the forward power provided by the RF energy sources is increased to compensate for the measured/estimated reflected power in order to produce the desired delivered power (i.e., delivered power=forward power−reflected power).
However, in semiconductor process chambers with two or more RF energy sources that produce at least one continuous wave and at least one pulsed wave, the delivered power is not consistent. Specifically, the continuous wave power is affected by pulsing of other energy source due to impedance change between “on” period and “off” period of pulsing.
Accordingly, the inventors have provided improved methods and apparatus for RF power delivery to provide more consistent delivered power in systems that use both at least one continuous wave and at least one pulsed wave.